A fully Cancer Center-managed facility, the Flow Cytometry Shared Resource assists HICCC members in flow cytometry-based studies. Services include: Fluorescence-activated cell sorting (FACS) Analytical flow cytometry for immunophenotyping Flow cytometry for analyzing cell cycle and apoptosis The capacity of the facility has increased substantially over the past three years due to the acquisition of new instruments. The facility now operates five instruments, including two fluorescence-activated cell sorters that allow high-speed cell sorting and can detect up to 12 fluorescent parameters, and one advanced cell analyzer that besides multi-color fluorescence is able to perform specialty applications such as determination of DMA content, multiple (living color) fluorescent protein analysis and calcium flux measurements. In addition to those sophisticated instruments, the facility provides access to two useroperated basic cytometers permitting 3 or 4 color immunophenotyping, respectively, as well as cell cycle and apoptosis assays. Over the last several years, the services of the facility have benefited 130 CUMC investigators, with HICCC members comprising the main users of the instruments accounting for ~60%. The high usage volume allows the facility to offer the services at low fees, which are further reduced for HICCC members. The sophisticated equipment available in the facility allows investigators at Columbia to perform state-of-the-art research in the area of flow cytometry, and therefore represent a vital resource for HICCC members. In the future, we plan to upgrade the flow cytometers to facilitate detection and sorting of newly developed living color fluorescent proteins and to purchase an instrument that serves as a flexible analysis platform for additional fluorescence-based techniques, including cytometric bead assays (CBA) to measure cytokine production, among other potential applications. During the last period of the CCSG, 36% of the investigators using the facility were Cancer Center members with peer-reviewed funding, with those members representing from 50% to 66% of the usage of the 3 available services. The proposed total operating budget of the facility is $425,004, of which we are requesting $ 116,271 from the CCSG